Polymethine dyes and ultraviolet (UV) absorbers containing a chromophore formed by an acidic electron accepting terminal nucleus and a basic electron donating terminal nucleus joined through a methine chain are well known. Such polymethines are commonly further categorized as merocyanines, hemioxonols, or merostyryls.
In merocyanines the basic terminal nucleus is a heterocyclic nucleus comprised of a five or six membered heterocyclic ring containing at least one nitrogen heteroatom. To achieve significant light absorption in the visible spectrum, thereby qualifying as a dye, the heterocyclic nucleus must exhibit aromaticity. In so-called zero methine merocyanines there are two methine groups linking the nuclei, but one linking methine group lies in the basic nucleus while the second linking methine group lies in the acidic nucleus. Thus, there are no methine groups separating the nuclei. Homologues of the zero methine merocyanines are those which contain two, four, or a higher even number of methine groups joining the terminal acidic and basic nuclei.
Hemioxonols can be viewed as differing from merocyanines in that their basic terminal nuclei take the form of aminomethine nuclei.
The acidic electron accepting terminal nucleus of each of these polymethines can be either heterocyclic or acyclic. When the acidic terminal nucleus is acyclic, it takes the form of a methylene group which is disubstituted with two strong electron withdrawing groups. The most commonly employed strong electron withdrawing groups are cyano, sulfo, and carbonyl groups, where the latter includes carboxylic acid and ester as well as acyl groups. Acylic acidic electron accepting terminal nuclei of polymethines are illustrated by
(R-1) Collins et al U.S. Pat. No. 2,411,507, PA0 (R-2) Kendall et al U.S. Pat. No. 2,511,210, PA0 (R-3) Kendall et al U.S. Pat. No. 2,693,472, PA0 (R-4) Edwards et al U.S. Pat. No. 2,721,799, PA0 (R-5) Kofron et al U.S. Pat. No. 4,439,520, and PA0 (R-6) Gunther et al U.S. Pat. No. 4,576,905. PA0 (R-7) Specht et al U.K. Pat. No. 3,083,832A, PA0 (R-8) Research Disclosure, Vol. 200, Dec. 1980, Item 20036, PA0 (A) Farid et al U.S. Ser. No. 933,712, filed Nov. 21, 1986, titled DYE SENSITIZED PHOTOGRAPHIC IMAGING SYSTEM, now U.S. Pat. No. 4,743,531; PA0 (B) Farid et al U.S. Ser. No. 933,658, filed Nov. 21, 1986, titled NEGATIVE WORKING PHOTORESISTS RESPONSIVE TO SHORTER VISIBLE WAVELENGTHS AND NOVEL COATED ARTICLES, now U.S. Pat. No. 4,743,529; PA0 (C) Farid et al U.S. Ser. No. 933,660, filed Nov. 21, 1986, titled NEGATIVE WORKING PHOTORESISTS RESPONSIVE TO LONGER VISIBLE WAVELENGTHS AND NOVEL COATED ARTICLES, now U.S. Pat. No. 4,743,530; PA0 (D) Farid et al U.S. Ser. No. 933,657, filed Nov. 21, 1986, titled ENHANCED IMAGING COMPOSITION CONTAINING AN AZINIUM ACTIVATOR, now U.S. Pat. No. 4,743,528. PA0 (R-9) U. Schollkopf, "Recent Applications of .alpha.-Metalated Isocyanides in Organic Synthesis", Angew. Chemie, Int. Ed., 1977, 16, 339-422. Note particularly compounds 9, 16, 17a, 17b, 18, 19, 32, and 34. PA0 (R-10) R. H. Hall et al, "Synthesis of C-Glycosyl Compounds. Part 1. Reaction of Ethylisocyanoacetate with 2,3,5,6-Di-O-isopropylidene-D-mannono-1,4-lactone", J. Chem. Soc., Perkin Trans. 1, 1977, 743-753. Note particularly compounds 6, 7, 11, and 12. PA0 (R-11) C. Herdeis et al, "Heterocyclic Substituted Amino Acids via .alpha.,.beta.-Dehydroamino Acid Derivatives. Studies on Amino Acids", Heterocycles, 1983, 20, 2163-2167. Note particularly compounds 3a and 3b. PA0 (R-12) Schollkopf et al, "Syntheses with .alpha.-Metalated Isocyanides, XLIV. Note on .beta.-Dimethylamino-.alpha.isocyanoacrylates and Their Use in Heterocyclic Chemistry", Justus Liebigs Ann. Chem., 1979, 1444-6. Note particularly compound 3. PA0 (R-13) Ugi Isonitrile Chemistry, Chapter 6, "The Reaction of Isonitriles with Boranes", Academic Press, 1971, New York and London. PA0 (R-14) Daniel et al U.S. Pat. No. 3,745,160, which discloses polymethine dyes containing 1,3,2-dioxaborinium, 1,3,2,-oxazoborinium, or 1,3,2-diazaborinium salt moieties. PA0 (R-15) Halm U.S. Pat. No. 4,123,268, which discloses 1,3,2-dioxaborinium salts as sensitizers in electrophotography. PA0 (R-16) Van Allen et al U.S. Pat. No. 4,394,428, which discloses polymethine dyes having a nucleus selected from the group consisting of 1,3,2-dioxaborin, 1,3,2-oxazoborin, and 1,3,2-diazoborin rings.
Polymethines with a basic electron donating terminal nucleus and an acidic terminal nucleus are known to serve a variety of uses. Such polymethines are known to be useful both as UV absorbers and dyes. These dyes and UV absorbers have been incorporated into photographic elements to serve a variety of purposes. In one application of particular interest these polymethines are incorporated in ultraviolet responsive imaging systems. Since ultraviolet light is both more energetic and capable of absorption with simpler molecular resonance structures than visible light, it is not surprising that there are a variety of known imaging materials which respond to ultraviolet, but not visible light. The sensitivity of these imaging systems can be extended to longer wavelength UV radiation and into the visible portion of the spectrum by incorporating a photosensitizer. Merocyanines have been extensively employed as photosensitizers and to a lesser extent (largely due to shorter wavelength absorption peaks) hemioxonols have been similarly employed.
Photographic silver halide emulsions are illustrative of imaging systems known to employ dyes from these polymethine classes as photosensitizers. The radiation sensitive silver halide grains present in photographic emulsions exhibit very limited absorption of radiation of wavelengths extending into the visible spectrum. However, with a dye adsorbed to the grain surfaces, the emulsions are highly responsive to visible light. The dye absorbs exposing photons and transfers either energy or an electron to the grain. The patents cited above disclose this photographic utility for merocyanine and hemioxonol dyes.
A variety of photographic imaging systems are known wherein a hardenable organic component containing ethylenic unsaturation sites is relied upon for image formation. The organic component undergoes photoinduced addition reactions, typically either polymerization or crosslinking, at the ethylenic unsaturation sites which produce hardening and allow image discrimination to be achieved.
It is common practice in preparing these compositions to employ coinitiators. One of the coinitiators is a photosensitizer. Photosensitizers are relied upon to capture photons of exposing radiation. The remaining coinitiator is referred to as an activator. The activator is not relied upon to respond directly to exposing radiation, but rather adjacent activator and photosensitizer molecules react, following excitation of the latter by photon capture, causing release by the activator of a free radical which in turn induces immobilizing addition reactions at sites of ethylenic unsaturation. The use of merocyanine dyes and UV absorbers as photosensitizers in such imaging systems is illustrated by
while the use of a variety of polymethine dyes as photosensitizers in such imaging systems are disclosed by the following four commonly assigned copending patent applications:
The polymethines of this invention are produced by first synthesizing corresponding polymethines containing an isocyano group as a part of the acidic terminal nucleus. The synthesis of dyes containing such an isocyano group is the subject of commonly assigned, concurrently filed patent application Ser. No. 067,843, titled NOVEL MEROCYANINE DYES AND IMAGING COMPOSITIONS, now abandoned in favor of continuation-in-part U.S. Ser. No. 183,876, filed Apr. 20, 1988.
The following illustrate known compounds containing isocyano groups:
A second step in preparing polymethines according to the present invention is to convert the acidic nucleus isocyano group of the corresponding polymethine to a triarylborylisocyano group. Polymethines containing a triarylborylisocyano group in the acidic terminal nucleus are the subject of commonly assigned, concurrently filed patent application Ser. No. 067,841, titled NOVEL POLYMETHINE DYES AND UV ABSORBERS AND IMAGING MATERIALS FOR THEIR USE.
the following illustrated known compounds containing boron atoms, particularly those containing boron atoms along with oxygen and/or nitrogen atoms in a ring structure: